1. Technical Field
The present invention relates to a lighting device and a projector.
2. Related Art
A projector is known as an apparatus displaying large-screen images. This projector includes a lighting device, an image forming device, a projection lens, and other units. Illumination light emitted from the lighting device is converted into image light representing images by the image forming device. This image light is expanded and projected by the projection lens such that large-screen images can be obtained more easily than a direct-viewing type image display apparatus.
For improving image quality of the projector, it is extremely important to equalize illuminance throughout a light receiving area of the image forming device illuminated by the lighting device. A fly-eye lens array is known as an illuminance equalizing element for equalizing illuminance of a lighting device including a lamp light source. A typical fly-eye lens array has a plurality of lenses, and two fly-eye lens arrays are used as pair units.
More specifically, light emitted from an arc tube included in the lighting device having the lamp light source is reflected by a reflector toward the axis of the arc tube (light source axis). The light released from the reflector is spatially divided into partial lights each of which enters the corresponding one of the plural lenses of a first fly-eye lens array. The plural lenses of the first fly-eye lens array converge the entering lights to the corresponding lenses of a second fly-eye lens array. The light converged by one lens of the first fly-eye lens array passes through one lens of the second fly-eye lens array, and illuminates the entire region of the light receiving area. The lights emitted from the respective lenses of the second fly-eye lens array are stacked (integrated) on the light receiving area to equalize the illuminance on the light receiving area.
With recent demand for a compact projector or for other reason, miniaturization of the lighting device has been expected. For example, a technology disclosed in JP-A-2001-242545 is an effective method for miniaturizing the lighting device. According to a light source provided with a reflector disclosed in JP-A-2001-242545, the reflector has plural divisional areas each of which is constituted by a part of a spheroid produced by rotating an ellipse around its axis.
The light source is disposed at first focus of the ellipse, and one lens constituting the fly-eye lens array is disposed at second focus of the ellipse. Light emitted from the light source is converged to one lens of the fly-eye lens array for each area of the reflector. Since the reflector also functions as one of the two fly-eye lens arrays, the corresponding fly-eye lens array can be eliminated.
According to the technology shown in JP-A-2001-242545, the size of the lighting device can be reduced. However, several points need to be improved to increase light utilization efficiency and equalize illuminance on the light receiving area.
According to the light source provided with the reflector shown in JP-A-2001-242545, the distances between the light source and the respective lenses of the fly-eye lens array differ according to the plural lenses. In this case, the focuses of the lights having passed the lenses differ according to the plural lenses, and thus the widths of the illumination ranges on the light receiving area differ according to the lenses.
In this case, illuminance on the peripheral portion of the light receiving area decreases for the entire stacked lights. When the peripheral area having lowered illuminance is used for illumination, the overall illuminance does not become uniform. When the peripheral area is not used for illumination, light utilization efficiency lowers.